Philip Johnston has been with the Daily Telegraph for more than 20 years. He is currently assistant editor and leader writer and was previously home affairs editor and chief political correspondent.

Gordon Brown should be wary of backing Ken Livingstone

Full coverage of UK politicsA big day in the contest to be Mayor of London. The latest opinion poll to be published by the London Evening Standard shows a 10-point lead for Boris Johnson, the Tory candidate seeking to end Ken Livingstone's eight-year tenure of City Hall.

Cameron supports his candidate; Brown shouldn't

This is slightly down on the 12-point lead he registered a fortnight ago but still suggests he is maintaining the momentum he has shown from the outset.

Boris has 47 per cent support to Mr Livingstone's 37 per cent, with Brian Paddick trailing badly with 10 per cent.

Johnson's campaign may have started looking like a job but it is deadly serious now.

As Charles Moore wrote in the Daily Telegraph on Saturday, the symbolic impact of a Boris victory would be a significant boost for the Tories and for David Cameron.

It is, therefore, odd that Gordon Brown should so publicly have endorsed Livingstone, a politician he has disliked for most of his career. He recently lavished praise on the Mayor, applauding his "lifelong commitment to London" which had enabled him "to get so much done for Londoners".Â He called him "an inspirational figure in London, a crusading mayor, and one that has made a huge difference".

Yet when Mr Livingstone stood as an independent in 2000 against Frank Dobson, the official Labour candidate, Mr Brown accused him of being "anti-jobs" and "anti-business". Mr Brown added: "Some people might think Ken Livingstone is funny, but saddling London with him for four years is no laughing matter."

Mr Livingstone responded by saying it was the then chancellor's own policies that were threatening London jobs.Â "It is Gordon Brown who has taxed business through his high interest rate and high exchange rate policies," he said.Â

The interesting thing about London is that for all that it is seen as unusual because of its cosmopolitan nature, it is electorally representative of the nation as a whole. In the period from 1992 to 2007, the share of the vote of the main political parties has largely reflected their performance nationally.

The significant shift that there has been towards the Tories in the South has also been apparent in London. Last year, the Conservatives won a majority of the 32 boroughs.

If Livingstone does secure a third term it would be portrayed less as a Labour win than as a personal triumph for the mayor after the difficulties he has faced in recent months. On the other hand, a Livingstone defeat would confirm that Labour's fortunes are in decline, possibly terminally.

Ken Livingstone, after all, is probably the most high-profile Labour politician after Gordon Brown. If he gets turfed out of office, there will be many Labour MPs worried that they will not get back into parliament after the next election, now likely in 2010.